1. Field of the Invention
The present invention relates to a swing measurement method of measuring a swing behavior of an impact implement, such as a golf club or a baseball bat having a grip portion, which is swung while the grip portion is being grasped. The swing measurement method is capable of directly and easily measuring the swing behavior without being influenced by flexure of the impact implement. In particular, the present invention relates to: a method of measuring the behavior of a golf swing directly and easily, without being influenced by the flexure of a golf shaft; to an analysis method capable of analyzing the golf swing behavior by a simple and effective model made from the obtained swing measurement data; and to a computer program product having computer program code causing a computer to analyze the golf swing behavior.
2. Description of the Related Art
Many types of golf clubs have been produced conventionally in order to pinpoint the direction of ball flight and to lengthen the carry. For example, golf clubs have been produced by considering static characteristics such as the shaft length of the golf club, the club weight, and the shaft stiffness. On the other hand, it is known that the form of the golf swing is an important element for making the flight direction of a hit ball more accurate, and for increasing the carry distance. Determining which golf club is suitable to an individual""s golf swing, from the many types of golf clubs available, has conventionally been an important concern for golfers. Therefore, in order to determine which golf club is suitable for an individual""s golf swing, it is desirable to directly and objectively know the characteristics of one""s individual golf swing, and to select the suitable golf club from the various golf clubs available based on that knowledge.
In an Unexamined Published Japanese Patent Application (Kokai) No. 10-244023, a method of selecting a golf club suitable to an individual""s swing was processed, by applying a strain gauge on a portion of a shaft of a golf club facing the direction of impact, and on a portion of the shaft facing the direction to which golfers face in an address state, perpendicular to the impact direction, measuring the deformation of the shaft during a swing from the output signals of the strain gauges during the swing and typifying the characteristics of the golf swing, and then choosing a golf club suitable to the individual""s swing from among various golf clubs based on the typified golf swing. In addition, an accompanying device or the like was also proposed.
On the other hand, in an Unexamined Published Japanese Patent Application (Kokai) No. 6-210027, a golf club design method capable of designing a golf club, in which a method of measuring a golf club by obtaining data for position and rotation angle by using a video camera in at least one location, such as on a shoulder, an elbow, or a wrist, then creating a model of a golfer from solid body elements such as beam elements, truss elements, or finite elements, and a model of a golf club, capable of design changes, by solid body elements such as finite elements, and then using the models to perform a simulation of the swing, was proposed. According to this proposal, it says it has become possible to select a golf club suitable to one""s individual swing by using this method.
In addition, in a Japanese Utility Model Registration No. 3050448, a device capable of validating swing form by photographing the swing form three dimensionally using a plurality of video cameras was this proposal, it says it has become possible to know the characteristics of one""s individual golf swing to a certain extent.
However, the above-mentioned method of measuring the deformation of the shaft during the swing by applying strain gauges to the shaft of the golf club do not directly measure the behavior of the actual swing. Rather, they estimate the swing form from deformed shape of the shaft by comparing various deformations of the shaft during conventionally typified swing forms and the measured deformation. Further, the time sequence data obtained is shaft strain data, so the golfer who swings the golf club cannot visually understand the result of the estimation.
Furthermore, in the method of validating the swing form by photographing the swing form three dimensionally by using a plurality of video cameras, the swing form is able to be directly seen, and the validation of the swing form and the swing form characteristics can easily be understood. However, it is not easy to set up the plurality of video cameras such that a blind spot does not develop during the swing. Further, the plurality of video cameras have to be synchronous each other, therefore the set up is not easy. Even if the video cameras are appropriately arranged so that a blind spot does not develop, for the data for the movement of the golf club head, a grip portion, and elbow and arm movement acquired sequentially in time, the resolution of the data is limited to be low. In particular, there are problems in that the rotation angle data, such as that for the wrist returning movement of the grip portion, is difficult to measure, and the measurement is performed with even lower precision. Furthermore, since many images are obtained using a plurality of video cameras, total amount of image data becomes enormous, and there becomes a problem that much efforts are needed in handling the enormous data for data processing.
With the method of performing a simulation by modeling the golfer using solid elements using elements such as beam elements, truss elements, or finite elements in order to investigate golf club behavior, data such as the physical data of the model and shape data must be input, and intricate preparations are necessary before performing the simulation. Furthermore, the swing characteristics cannot be typified simply with a solid body model using beam elements, truss elements, or finite elements.
The above problems which thus arise during the measurement of the swing form are not limited to the golf swing, and there are common problems in various swings using an impact implement, such as a baseball bat swing, a tennis racket swing, and a badminton racket swing.
The present invention has been made to solve the above-mentioned problem, and therefore has an object to provide a swing measurement method capable of easily obtaining time sequence measurement data by directly measuring a swing behavior of an impact implement having a grip portion, such as a baseball bat, a tennis racket, or a badminton racket, when the grip portion is grasped and swung, without being influenced by flexure of the impact implement. In particular, an object of the present invention is to provide a swing measurement method capable of easily obtaining time sequence measurement data by directly measuring a golf swing behavior of a golfer without being influenced by flexure due to a golf shaft. In addition, an object of the present invention is to provide a method of analyzing a golf swing capable of obtaining the behavior of a golf club grip portion using a simple and effective model, without using a solid element model such as a beam element, a truss element, or a finite element model.
In order to achieve the above and other objects, according to a first aspect of the present invention, there is provided a swing measurement method for measuring a swing behavior during a swing with an impact implement grasped on a grip portion thereof, comprising the steps of fixing a three dimensional magnetic sensor to the grip portion of the impact implement, forming magnetic fields, each distribution of intensity and direction thereof being known, within a range of motion of the grip portion, so that the three dimensional magnetic sensor senses magnetism of each of the formed magnetic fields for outputting signals corresponding to three dimensional position of the grip portion with respect to a predetermined point, and to pointing direction of the grip portion with respect to a predetermined direction, and acquiring at least one of three dimensional position coordinates data of the grip portion and pointing direction data of the grip portion from the output signals.
In particular, the impact implement is a golf club, and the three dimensional position coordinates data and the pointing direction data, are acquired during the swing of the golf club.
Further, it is preferable that the three dimensional position coordinates data and the pointing direction data, represent the swing behavior of the grip portion at least from a top state to an impact state of the swing.
Further, it is preferable that the three dimensional magnetic sensor fixed to the grip portion has three mutually orthogonal axes for sensing, one direction of an axis from among the three mutually orthogonal axes being aligned with a direction of an axis of a shaft of the golf club, and one direction of an axis from among the other two axes being aligned with an impact direction of the golf club.
Further, it is preferable that the three dimensional magnetic sensor is fixed to the end of the grip portion.
Further, according to a second aspect of the present invention, there is provided a golf swing analysis method for analyzing a swing behavior of a golf club, comprising the steps of receiving time sequence data of three dimensional position coordinates of a grip portion of the golf club, and time sequence data of pointing direction of the grip portion during a golf swing from a data acquisition means, calculating a swing plane, on which a swing path of the grip portion is approximated, from the time sequence data of the three dimensional position coordinates, projecting the swing path of the grip portion on the swing plane and approximating the projected swing path as an arc to obtain the arc as a swing path arc of the grip portion, and obtaining arm angle time sequence data of an arm angle showing a position of the grip portion on the swing plane from the time sequence data of three dimensional position coordinates and the swing path arc, and at least one time sequence data from the group consisting of wrist angle time sequence data of a wrist angle found based on a shaft direction angle obtained from the pointing direction of the grip portion and showing a shaft direction of the golf club on the swing plane, and rotation angle time sequence data of a shaft rotation angle, around a shaft axis of the golf club, from the pointing direction.
It is preferable that the wrist angle is found by subtracting the arm angle from the shaft direction angle.
It is also preferable that the swing plane of the grip portion is calculated using the swing path of the grip portion including the swing behavior at least from a top state of the golf swing to an impact state.
Further, it is also preferable that the swing path arc of the grip portion is calculated using the projected swing path including the swing behavior at least from a top state of the golf swing to an impact state.
Further, it is preferable that the arm angle time sequence data, and at least one of the wrist angle time sequence data and the rotation angle time sequence data, represent the swing behavior at least from a top state of the golf swing to an impact state.
Further, it is preferable that the swing behavior of the grip portion is analyzed by plotting at least one time sequence data, from among the wrist angle time sequence data and the rotation angle time sequence data, against the arm angle time sequence data.
Further, it is preferable that the data acquisition means has a three dimensional magnetic sensor and a means for forming magnetic fields, each distribution of intensity and direction thereof being known, so that the three dimensional magnetic sensor senses magnetism of each of the formed magnetic fields for outputting signals corresponding to three dimensional position of the three dimensional magnetic sensor with respect to a predetermined point, and to pointing direction of the three dimensional magnetic sensor with respect to a predetermined direction, acquires the time sequence data of the three dimensional position coordinates and the time sequence data of the pointing direction, by fixing the three dimensional magnetic sensor to the grip portion and forming the magnetic fields within a range of motion of the grip portion during the golf swing.
It is also preferable that the data acquisition means uses at least one camera from the group consisting of a high speed camera, a CCD camera, and a strobe photography camera, and the time sequence data of the three dimensional position coordinates and the time sequence data of the pointing direction during the golf swing, are acquired by performing measurements from images obtained by the camera.
Furthermore, according to a third aspect of the present invention, there is provided a computer program product, comprising a computer readable medium having computer program code embodied for an analysis of swing behavior of a golf club, the computer program code including computer program code configured to cause a computer to receive time sequence data of three dimensional position coordinates of a grip portion of the golf club and time sequence data of pointing direction of the grip portion during a golf swing from a data acquisition means, computer program code configured to cause a computer to compute a swing plane, on which a swing path of the grip portion is approximated, from the time sequence data of the three dimensional position coordinates, computer program code configured to cause a computer to project the swing path of the grip portion on the swing plane and approximate the projected swing path as an arc to obtain the arc as a swing path arc of the grip portion, and computer program code configured to cause a computer to obtain arm angle time sequence data of an arm angle showing a position of the grip portion on the swing plane from the time sequence data of the three dimensional position data and the swing path arc, and at least one time sequence data from the group consisting of wrist angle time sequence data of an wrist angle found based on a shaft direction angle obtained from the time sequence data of the pointing direction and showing a shaft direction of the golf club on the swing plane, and rotation angle time sequence data of a shaft rotation angle, around a shaft axis of the golf club, from the pointing direction.
It is preferable that the wrist angle is found by subtracting the arm angle from the shaft direction angle.
Further, it is preferable that the swing plane is computed using the swing path of the grip portion including the swing behavior at least from a top state of the golf swing to an impact state.
It is preferable that the swing path arc of the grip portion is computed using the projected swing path including the swing behavior at least from a top state of the golf swing to an impact state.
It is also preferable that the arm angle time sequence data, and at least one of the wrist angle time sequence data and the rotation angle time sequence data, represent the swing behavior at least from a top state of the golf swing to an impact state.
Further, it is preferable that the computer program code also includes computer program code configured to cause a computer to plot at least one time sequence data, from among the wrist angle time sequence data and the rotation angle time sequence data, against the arm angle time sequence data.